17,081 research outputs found
The Application of a Cylindrical-spherical Floating Ring Bearing as a Device to Control Stability of Turbogenerators
The development of a new device to control stability of turbogenerators is described. The device comprises a floating ring installed between the journal and bearing housing of a fluid film bearing. The journal and the inner surface of the ring are cylindrical while the outer surface of the ring and bearing surface are spherical providing axial location of the ring and self-alignment of the bearing. The employment of this device would lead to a consistent machine performance. System stability may be controlled by changing a number of bearing and floating ring parameters. This device also offers an additional advantage of having a very low frictional characteristic. A feasibility study was carried out to investigate the suitability of the new device to turbogenerator applications. Both theoretical analysis and experimental observations were carried out. Initial results suggest that the new floating ring device is a competitive alternative to other conventional arrangements
Quantum Entanglement Capacity with Classical Feedback
For any quantum discrete memoryless channel, we define a quantity called
quantum entanglement capacity with classical feedback (), and we show that
this quantity lies between two other well-studied quantities. These two
quantities - namely the quantum capacity assisted by two-way classical
communication () and the quantum capacity with classical feedback ()
- are widely conjectured to be different: there exists quantum discrete
memoryless channel for which . We then present a general scheme to
convert any quantum error-correcting codes into adaptive protocols for this
newly-defined quantity of the quantum depolarizing channel, and illustrate with
Cat (repetition) code and Shor code. We contrast the present notion with
entanglement purification protocols by showing that whilst the Leung-Shor
protocol can be applied directly, recurrence methods need to be supplemented
with other techniques but at the same time offer a way to improve the
aforementioned Cat code. For the quantum depolarizing channel, we prove a
formula that gives lower bounds on the quantum capacity with classical feedback
from any protocols. We then apply this formula to the protocols
that we discuss to obtain new lower bounds on the quantum capacity with
classical feedback of the quantum depolarizing channel
Geodesic Distance Histogram Feature for Video Segmentation
This paper proposes a geodesic-distance-based feature that encodes global
information for improved video segmentation algorithms. The feature is a joint
histogram of intensity and geodesic distances, where the geodesic distances are
computed as the shortest paths between superpixels via their boundaries. We
also incorporate adaptive voting weights and spatial pyramid configurations to
include spatial information into the geodesic histogram feature and show that
this further improves results. The feature is generic and can be used as part
of various algorithms. In experiments, we test the geodesic histogram feature
by incorporating it into two existing video segmentation frameworks. This leads
to significantly better performance in 3D video segmentation benchmarks on two
datasets
Absence of hole pairing in a simple t-J model on the Shastry-Sutherland lattice
The Shastry-Sutherland model is a two-dimensional frustrated spin model whose
ground state is a spin gap state. We study this model doped with one and two
holes on a 32-site lattice using exact diagonalization. When t'>0, we find that
the diagonal dimer order that exists at half-filling are retained at these
moderate doping levels. No other order is found to be favored on doping. The
holes are strongly repulsive unless the hopping terms are unrealistically
small. Therefore, the existence of a spin gap at half-filling does not
guarantee hole-pairing in the present case
Spiral cracks in drying precipitates
We investigate the formation of spiral crack patterns during the desiccation
of thin layers of precipitates in contact with a substrate. This
symmetry-breaking fracturing mode is found to arise naturally not from torsion
forces, but from a propagating stress front induced by the fold-up of the
fragments. We model their formation mechanism using a coarse-grain model for
fragmentation and successfully reproduce the spiral cracks. Fittings of
experimental and simulation data show that the spirals are logarithmic,
corresponding to constant deviation from a circular crack path. Theoretical
aspects of the logarithmic spirals are discussed. In particular we show that
this occurs generally when the crack speed is proportional to the propagating
speed of stress front.Comment: 4 pages, 5 figures, RevTe
Perturbative Approach to the Quasinormal Modes of Dirty Black Holes
Using a recently developed perturbation theory for uasinormal modes (QNM's),
we evaluate the shifts in the real and imaginary parts of the QNM frequencies
due to a quasi-static perturbation of the black hole spacetime. We show the
perturbed QNM spectrum of a black hole can have interesting features using a
simple model based on the scalar wave equation.Comment: Published in PR
Quasi-Normal Mode Expansion for Linearized Waves in Gravitational Systems
The quasinormal modes (QNM's) of gravitational systems modeled by the
Klein-Gordon equation with effective potentials are studied in analogy to the
QNM's of optical cavities. Conditions are given for the QNM's to form a
complete set, i.e., for the Green's function to be expressible as a sum over
QNM's, answering a conjecture by Price and Husain [Phys. Rev. Lett. {\bf 68},
1973 (1992)]. In the cases where the QNM sum is divergent, procedures for
regularization are given. The crucial condition for completeness is the
existence of spatial discontinuities in the system, e.g., the discontinuity at
the stellar surface in the model of Price and Husain.Comment: 12 pages, WUGRAV-94-
Efficiency of feedback process in cavity quantum electrodynamics
Utilizing the continuous frequency mode quantization scheme, we study from
first principle the efficiency of a feedback scheme that can generate maximally
entangled states of two atoms in an optical cavity through their interactions
with a single input photon. The spectral function of the photon emitted from
the cavity, which will be used as the input of the next round in the feedback
process, is obtained analytically. We find that the spectral function of the
photon is modified in each round and deviates from the original one. The
efficiency of the feedback scheme consequently deteriorates gradually after
several rounds of operation.Comment: 11 pages, 5 figures, accepted for publication in Journal of Physics
C60 adsorption on an aperiodically modulated Cu surface
Copper deposited on the ve-fold surface of icosahedral Al-Pd-Mn forms domains of a structure whose surface has a one-dimensional aperiodic modulation. It is shown that C60
deposited on this aperiodic film has highly reduced mobility as compared to C60 deposited on periodic Cu surfaces. This fnding is explained in terms of the recently proposed structural model of this system
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